1. Field of the Invention
The invention relates to a spoke for a spoked wheel. It also relates to its method of manufacture and to a wheel equipped with at least one such spoke.
2. Description of Background and Other Information
Conventionally, each of the spokes of a spoked wheel include an elongated body and, at opposite ends of the body, a head end and a fastening end, allowing the tension of the spoke to be adjusted. Conventionally, such spokes are made of metal, although spokes are also known to be made of composite material which provides the advantage of relative lightness and increased strength.
The patent document WO 91/13771 and U.S. Pat. No. 5,110,190 disclose such a spoke formed of synthetic fibers having a high modulus of elasticity.
The patent documents FR 2 586 378, EP 165 590, and JP 60080901 disclose composite spokes whose body is made of synthetic fibers embedded in a resin matrix. An end piece, generally metallic, is attached to each end of the body to form the spoke head and the fastening end. The assembly between the body and the end pieces is carried out by gluing or crimping. Using composite material for the body of the spoke makes it possible to reduce the weight while maintaining the desired mechanical properties (rigidity, fatigue-strength).
However, these methods of construction are not entirely satisfactory. In order to reduce the weight of the spoke, and because of the material used, the body cross section has a reduced diameter, such as, for example 2 millimeters (mm) or about 2 mm. Under these circumstances, the assembly between the body and the end pieces lacks sturdiness. Indeed, due to the narrow cross section of the body, the surface area between these elements is also small. The surface area could be extended to increase its size, which would however negate the desired lightness since this would augment the size of the metal end pieces, which are heavier. Further, extending the gluing surface is, from a practical standpoint, not sufficient to withstand the stresses once the spoke is tensioned. In the embodiment shown in EP 165 590, the constituent fibers of a spoke are small in diameter and, therefore, have a low resistance to shearing and torsion. This results, most of the time, in the spoke breaking when tensioned due to the frictional torque generating the torsion.
In view of this state of the art, there is a need for a spoke that is improved to provide a sturdier assembly between the body and the end pieces.